Load control and holding valve

ABSTRACT

A load control and holding valve having a counterbalance valve with a check valve coaxially therewithin, both valves being closed to lock a fluid motor against downward drift of a load acting thereon. The counterbalance valve comprises a body having a stepped bore with a seat at its small end, and a stepped counterbalance valve member which is spring biased into engagement with the body seat and which has a first relatively small annular area exposed to motor load pressure to open said member in the event of overload due to shock load, load inertia, or thermal expansion of the fluid between the motor and the counterbalance valve. The counterbalance valve member also has a second relatively larger annular area which is exposed to pilot pressure derived from the pressure side of the motor to open the return side of the motor when the load is raised and to throttle or shut off the return side when the load tends to run ahead of the pump. The counterbalance valve member has, its small end, a check valve seat against which is seated a check valve member which permits flow to the motor when it is desired to reverse the direction of actuation of the motor.

United States Patent [72] Inventor George J. Martin Lyndhurst, Ohio [21] Appl. No. 1,716 [22] Filed Jan. 9, 1970 [45] Patented July 27, 1971 [73] Assignee Parker-llannifin Corporation Cleveland, Ohio [54] LOAD CONTROL AND HOLDING VALVE 10 Claims, 2 Drawing Figs.

[52] U.S. Cl 137/493, l37/495 [51] Int.Cl Flfik 17/18 [50] Field of Search l37/493.6, 493, 495

[56] References Cited V UNITED STATES PATENTS 3,349,671 l0/l967 Hoffman 137/493 X Primary Examiner-M. Cary Nelson Assislan! Examiner-R. B. Rothman Attorney-Oberlin. Maky. Donnelly & Renner ABSTRACT: A load control and holding valve having a counterbalance valve with a check valve coaxially therewithin, both valves being closed to lock a fluid motor against downward drift of a load acting thereon. The counterbalance valve comprises a body having a stepped bore with a seat at its small end, and a stepped counterbalance valve member which is spring biased into engagement with the body seat and which has a first relatively small annular area exposed to motor load pressure to open said member in the event of overload due to shock load, load inertia, or thennal expansion of the fluid between the motor and the counterbalance valve. The counterbalance valve member also has a second relatively larger annular area which is exposed to pilot pressure derived from the pressure side of the motor to open the return side of the motor when the load is raised and to throttle or shut off the return side when the load tends to run ahead of the pump. The counterbalance valve member has, its small end, a check valve seat against which is seated a check valve member which permits flow to the motor when it is desired to reverse the direction of actuation of the motor.

LOAD CONTROL AND HOLDING VALVE BACKGROUND OF THE INVENTION In an aerial lift device (see for example the US. Pat. to Schmiel et al. No. 3,373,843, granted Mar. 19, I968), as the boom moves over center, the load on the boom actuating fluid motor changes from positive to negative and when that occurs, the load tends to run ahead of the pump thus to cause cavitation or reduction of pressure on the pressure side of the motor with consequent loss of control of the load-lowering operation. It is known to provide in an aerial lift device or other hydraulically actuated device wherein there is a tendency of a load running ahead of the pump to provide a socalled overcenter valve which includes a piloted counterbalance valve for permitting return flow from the motor only when there is a predetermined positive pilot pressure acting thereon from the pressure side of the motor, and a check valve for permitting pump flow into the motor for reversing the direction of actuation of the motor.

However, in known overcenter valves which are used to prevent a motor load from running ahead of the pump, and to lock the load in any position without drift while providing for overload and thermal relief, the counterbalance and check valves are separated from each other in laterally spaced apart or in angular relation. Such arrangement of the counterbalance check valves complicates the housing construction to provide the various fluid flow passages, the check valve and counterbalance valve bores and seats, and the spring backup plugs for closing the valve bores.

In other known overcenter valves wherein the counterbalance and check valves are disposed concentrically one within the other, the plunger portion acted upon by pilot pressure moves the counterbalance valve in the same direction as the flow of fluid from the fluid motor whereby it tends to stay open despite substantial decrease in pilot pressure subsequent to initial opening.

SUMMARY OF THE INVENTION In contrast with the foregoing, the present overcenter valve is of simple compact structure in which the valve body is provided with a stepped bore terminating at its small end in a valve seat and a valve port for connection with a directional control valve and intersected at different diameters by a motor port and a pilot port, At the large end of the bore is a spring backup'and' adjusting mechanism. The counterbalance valve member is of steppedform having a seat at its small end for engagement with said valve seat and defines with the stepped bore a first relatively small annular'area which is exposed to pressure in the motor port due to motor load, and a second relatively large annular area which is exposed to pilot pressure from the inlet or pressure side of the fluid motor whereby said counterbalance valve member is moved to open position when the sum of these forces exceeds a predetermined value as determined by a spring acting thereon. In the present overcenter valve the check valve member is seated within the small end of the counterbalance valve member so as to open in the same direction as the opening movement of the counterbalance valve member.

Other objects and advantages of the present invention will appear hereinafter.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a schematic diagram illustrating a hydraulic system employing two overcenter valves to handle loads which tend to overrun in both directions past center; and

FIG. 2 is a central cross section view of the overcenter valve constituting the present invention DETAILED DESCRIPTION OF THE INVENTION In FIG. I the reference numeral 1 denotes a double-acting fluid motor for actuating the boom 2 of an aerial lift device or the like between the solid line and dot-dash line positions and as evident, if the boom 2 is being swung in a clockwise direction from the solid line position the load is positive until the vertical position is passed and thereafter the load is nega' tive and thus tends to pull the piston 3 toward the right with consequent pressure drop or cavitation in the head end of the cylinder 1, except for the provision of the overcenter valve 4 herein. If the overrunning load acts only in one direction, then only a single overcenter valve 4 is necessary but if the overrunning load acts in both directions as herein shown, then another overcenter valve 4 is provided in association with the other end of the motor I. In such case, both overcenter valves 4 may be built into a single valve body.

When the boom 2 is to be actuated in a clockwise direction, the four-way open center valve 5 will be shifted toward the right whereby fluid discharged under pressure from the pump 6 will flow through the four-way valve 5, through the conduit 7, the check valve section of the left-hand overcenter valve 4, and the conduit 8 into the head end of the motor 1. Pilot pressure in the conduit 9 is conducted to the pilot port of the righthand overcenter valve 4 and when that pilot pressure, and thus the pressure in conduit 7 is of predetermined magnitude as hereinafter explained in detail, the counterbalance valve member in the right-hand overcenter valve 4 will be opened to permit return flow from the rod end of the motor 1 to the tank 10 via the conduit I I and 12 and the four-way valve 5.

When the four-way valve 5 is shiftedrto the left from its neutral position, the motor 1 is actuated in the opposite direction to swing the boom 2 in a counterclockwise direction with fluid under pressure flowing through the conduit 12, the check valve section of the right-hand overcenter valve 4, and the conduit 11 into the rod end of the motor 1, and the return fluid from the head end of the motor 1 is returned to the tank 10 via the counterbalance valve in the left-hand overcenter valve 4 which is opened by pilot pressure in the conduit 14 and the pressure supply conduit 12. Referring now to FIG. 2, the overcenter valve 4 comprises a valve body 15 having a stepped bore 16 which terminates at its small end in a counterbalance valve seat 17 and a valve port 18 for connection with a motor port of the four-way valve 5, the stepped bore 16 being intersected by a cylinder port 19 and a pilot port 20. The large end of the stepped bore 16 is threaded for receipt of a cap 21 and an adjusting screw 23 is threaded into said cap 21 to adjust the compression of the spring 24 which biases the counterbalance valve member 25 into engagement with the seat member 17.

When the load on the motor 1 is in overrunning position, the pressure due to the load acts on the annular area of diameter A minus diameter B of the counterbalance valve member 25 tending to move said member 25 away from the seat 17. However, that area is not sufficient to compress the spring 24 except when the four-way valve 5 is shifted to neutral to stop movement of the load, whereby inertia forces may build up momentarily to a high pressure sufficient to open the counterbalance valve member 25. When the load is locked in desired position, the counterbalance valve member 25 acts not only as an overload relief valve during stopping of the load, as aforesaid, but also as a thermal relief valve to permit expansion of the liquid due to temperature increase thereof. To open the counterbalance valve member 25 under conditions of overrunning load on the motor 1 requires that there be sufficient pressure in the pressure side of the motor 1 such that the pilot pressure in the port 20 acting on the substantially larger annular area of diameter C minus diameter A is sufficient together with the load pressure, to move the counterbalance valve member 25 to open position, thus to allow return flow of oil from the motor 1 to the tank 10 via the fourway valve 5, and counterbalance valve 25.

The small end of the counterbalance valve member 25 has a seat 26 against which a check valve member 27 is biased by the spring 28. The spring backup member 29 is sealed in the bore of the counterbalance valve member 25 and said backup member 29 is retained by a cross pin 30 extending diametrically across the counterbalance valve member'25.

When the boom 2 is to be swung in a counterclockwise direction, the four-way valve 5 will be shifted toward the left from the FIG. 1 neutral position whereby fluid under pressure in the valve port 18 will unseat the check valve member 27 to permit flow through the cylinder port 19 to the rod end of the motor 1 and if there were no overrunning condition encountered in counterclockwise actuation of the boom 2, the fluid in the head end of the motor 1 would be returned directly to the tank via the four-way valve 5, there then being no necessity for providing an overcenter valve as shown at the left in FIG. 1. However, if there is an overrunning condition during counterclockwise swinging of the boom, then the pilot pressure in conduit 14 and load pressure in conduit 8 when it reaches a predetermined value will open the counterbalance valve member 25 in the left-hand overcenter valve 4 to permit return flow to the tank 10 via the four-way valve 5. Generally, the annular area CA which is exposed to pilot pressure will be several times the annular area A-B which is exposed to load pressure. For example, the pilot ratio may be, say, 10:1 whereby, for example, if the overload relief and thermal relief and thermal relief setting (area A-B) of the spring 24 were 2,000 p.s.i. and if the load pressure on the annular area AB were say, 1,000 p.s.i., then a pilot pressure in excess of l00 p.s.i. in conduit 9 (or conduit 14) would be required to effect opening movement of the counterbalance valve member 25. If. the pilot pressure in port decreases, the counterbalance valve member will move toward seated position, thus to throttle the return flow and maintain controlled lowering of the load and preventing cavitation on the pump or pressure side of the motor I.

The spring chamber 31 may be vented directly to the tank 10 or may be vented to the valve port 18 as by means of the passage 32 in the body 15.

Of course, when the load on motor 1 is being raised, then the pilot pressure itself builds up sufficiently to open the counterbalance valve member 25. When said member 25 is open, return flow is substantially unimpeded except for back pressure due to return line losses, so that maximum power is available for raising the load.

I, therefore, particularly point out and distinctly claim as my invention:

1. A valve assembly comprising a body having a stepped bore terminating at its small end in a valve seat and a valve port for connection to a directional control valve, said body having a motor port and a pilot port leading to different diameter portions of said bore and adapted to be connected to the respective ports ofa double acting fluid motor; a counterbalance valve member movable in said bore into and out of engagement with said seat and defining with said bore first and second annular areas which are exposed to fluid pressure in said motor and pilot ports respectively; spring means biasing said valve member into engagement with said seat to prevent flow of fluid from said motor port to said valve port except when fluid pressure in said motor port due to thermal expansion of the fluid or to motor load inertia or shock is of magnitude sufficient to overcome the bias of said spring means thus to move said valve member out of engagement with said seat for relief of excess pressure through said motor and valve ports and except when fluid pressure in said pilot port from the pressure side of the fluid motor is of magnitude sufficient to overcome the bias of said spring means thus to permit return flow of fluid from the motor through said motor and valve ports; and a check valve member movable in said counterbalance valve member to permit flow of fluid in the opposite direction from said valve port to said motor port.

2. The valve assembly of claim 1 wherein said counterbalance valve member is moved out of engagement with said seat by the conjoint effect of motor load pressure and pilot pressure respectively acting on said first and second annular areas.

3. The valve assembly of claim 1 wherein said second annular area is larger than said first annular area.

4. The valve assembly of claim 1 wherein said counterbalance valve member is tubular at its small end and has an internal seat for said check valve member and a passage through the wall thereof for communicating said valve and motor ports with each other when said check valve member is moved away from said internal seat.

5. A valve assembly comprising a body having a bore terminating at one end in a valve seat and a valve port for connection to a directional control valve, said body having a motor port and a pilot port leading to axially spaced-apart portions of said bore and adapted to be connected to the respective ports of a double acting fluid motor; a counterbalance valve member movable in said bore into and out of engagement with said seat and defining with said bore first and second annular areas which are exposed to fluid pressure in said motor and pilot ports respectively; spring means biasing said valve member in engagement with said seat to prevent flow of fluid from said motor port to said valve port except when fluid pressure in said motor port due to thermal expansion of the fluid or to motor load inertia or shock is of magnitude sufficient to overcome the bias of said spring means thus to move said valve member out of engagement with said seat for relief of excess pressure through said motor and valve ports and except when fluid pressure in said pilot port from the pressure side of the fluid motor is of magnitude sufficient to overcome the bias of said spring means thus to permit return flow of fluid from the motor through said motor and valve ports; and a check valve member movable in said counterbalance valve member to permit flow of fluid in the opposite direction from said valve port to said motor port.

6. The valve assembly of claim 5 wherein said body has cap means closing the other end of said bore; and wherein said cap means has adjusting screw means bearing on said spring means to vary the overload pressure in said motor port and the pilot pressure in said pilot port at which said counterbalance valve member is moved out ofengagement with said seat.

7. A valve assembly comprising a body having a stepped bore terminating at its small end in a valve seat and a valve port for connection to a directional control valve, said body having a motor port and a pilot port leading to different diameter portions of said bore and adapted to be connected to the respective ports ofa double acting fluid motor and having closure means at the large end of said bore; a counterbalance valve member movable in said bore into and out of engagement with said seat and defining with said bore first and second annular areas which are exposed to fluid pressure in said motor and pilot ports respectively, and defining with the large end of said bore and closure means a chamber which is in fluid communication with said valve port; spring means in said chamber biasing said valve member into engagement with said seat to prevent flow of fluid from said motor port to said valve port except when fluid pressure in said motor port due to thermal expansion of the fluid or to motor load inertia or shock is of magnitude sufficient to overcome the bias of said spring means thus to move said valve member out of engagement with said seat for relief of excess pressure through said motor and valve ports and except when the fluid pressure in said pilot port from the pressure side of the fluid motor is of magnitude sufficient to overcome the bias of said spring means thus to permit return flow of fluid from the motor through said motor and valve ports; and a check valve member movable in said counterbalance valve member to permit flow of fluid in the opposite direction from said valve port to said motor port.

8. The valve assembly of claim 7 wherein said counterbalance valve member has tubular end portions with partition means therebetween; said check valve member being located in the small end of said counterbalance valve member to engage an internal seat therein; and wherein another spring means between said check valve member and said partition means biases the former into engagement with said internal seat.

.9. The valve assembly of claim 8 wherein said spring means for biasing said counterbalancevalve member extends into the large tubular end portion to bear on said counterbalance valve member; and wherein said closure means has adjusting screw means bearing on said spring means for varying the degree of biasing of said counterbalance valve member.

10. A valve assembly comprising a body having a stepped bore terminating at its small end in a valve seat and a valve port for connection to a directional control valve, said body having a motor port and a pilot port leading to different diameter portions of said bore and adapted to be connected to the respective ports of a double acting fluid motor; a stepped counterbalance valve member in said bore spring biased into engagement with said seat to prevent return flow of fluid from said motor port to said valve port; said valve member having a first relatively small annular area defined between said valve seat and a first enlargement of said bore which is exposed to fluid pressure in said motor port, whereby fluid pressure of relatively large magnitude due to thermal expansion of the fluid or to motor load inertia or shock will overcome the spring bias to move said valve member away from said seat for relief of excess pressure through said motor and valve ports, and a second relatively large annular area defined between said first enlargement of said bore and a second enlargement thereof which is exposed to fluid pressure in said pilot port whereby fluid pressure in said pilot port of relatively low magnitude will overcome the spring bias to move said valve member as aforesaid for return flow of fluid from the motor through said motor and valve ports; and a check valve member movable in said counterbalance valve member to permitflow of fluid in the opposite direction from said valve port to said motor port. 

1. A valve assembly comprising a body having a stepped bore terminating at its small end in a valve seat and a valve port for connection to a directional control valve, said body having a motor port and a pilot port leading to different diameter portions of said bore and adapted to be connected to the respective ports of a double acting fluid motor; a counterbalance valve member movable in said bore into and out of engagement with said seat and defining with said bore first and second annular areas which are exposed to fluid pressure in said motor and pilot ports respectively; spring means biasing said valve member into engagement with said seat to prevent flow of fluid from said motor port to said valve port except when fluid pressure in said motor port due to thermal expansion of the fluid or to motor load inertia or shock is of magnitude sufficient to overcome the bias of said spring means thus to move said valve member out of engagement with said seat for relief of excess pressure through said motor and valve ports and except when fluid pressure in said pilot port from the pressure side of the fluid motor is of magnitude sufficient to overcome the bias of said spring means thus to permit return flow of fluid from the motor through said motor and valve ports; and a check valve member movable in said counterbalance valve member to permit flow of fluid in the opposite direction from said valve port to said motor port.
 2. The valve assembly of claim 1 wherein said counterbalance valve member is moved out of engagement with said seat by the conjoint effect of motor load pressure and pilot pressure respectively acting on said first and second annular areas.
 3. The valve assembly of claim 1 wherein said second annular area is larger than said first annular area.
 4. The valve assembly of claim 1 wherein said counterbalance valve member is tubular at its small end and has an internal seat for said check valve member and a passage through the wall thereof for communicating said valve and motor ports with each other when said check valve member is moved away from said internal seat.
 5. A valve assembly comprising a body having a bore terminating at one end in a valve seat and a valve port for connection to a directional control valve, said body having a motor port and a pilot port leading to axially spaced-apart portions of said bore and adapted to be connected to the respective ports of a double acting fluid motor; a counterbalance valve member movable in said bore into and out of engagement with said seat and defining with said bore first and second annular areas which are exposed to fluid pressure in said motor and pilot ports respectively; spring means biasing said valve member in engagement with said seat to prevent flow of fluid from said motor port to said valve port except when fluid pressure in said motor port due to thermal expansion of the fluid or to motor load inertia or shock is of magnitude sufficient to overcome the bias of said spring means thus to move said valve member out of engagement with said seat for relief of excess pressure through said motor and valve ports and except when fluid pressure in said pilot port from the pressure side of the fluid motor is of magnitude sufficient to overcome the bias of said spring means thus to permit return flow of fluid from the motor through said motor and valve ports; and a check valve member movable in said counterbalance valve member to permit flow of fluid in the opposite direction from said valve port to said motor port.
 6. The valve assembly of claim 5 wherein said body has cap means closing the other end of said bore; and wherein said cap means has adjusting screw means bearing on said spring means to vary the overload pressure in said motor port and the pilot pressure in said pilot port at which said counterbalance valve member is moved out of engagement with said seat.
 7. A valve assembly comprising a body having a stepped bore terminating at its small end iN a valve seat and a valve port for connection to a directional control valve, said body having a motor port and a pilot port leading to different diameter portions of said bore and adapted to be connected to the respective ports of a double acting fluid motor and having closure means at the large end of said bore; a counterbalance valve member movable in said bore into and out of engagement with said seat and defining with said bore first and second annular areas which are exposed to fluid pressure in said motor and pilot ports respectively, and defining with the large end of said bore and closure means a chamber which is in fluid communication with said valve port; spring means in said chamber biasing said valve member into engagement with said seat to prevent flow of fluid from said motor port to said valve port except when fluid pressure in said motor port due to thermal expansion of the fluid or to motor load inertia or shock is of magnitude sufficient to overcome the bias of said spring means thus to move said valve member out of engagement with said seat for relief of excess pressure through said motor and valve ports and except when the fluid pressure in said pilot port from the pressure side of the fluid motor is of magnitude sufficient to overcome the bias of said spring means thus to permit return flow of fluid from the motor through said motor and valve ports; and a check valve member movable in said counterbalance valve member to permit flow of fluid in the opposite direction from said valve port to said motor port.
 8. The valve assembly of claim 7 wherein said counterbalance valve member has tubular end portions with partition means therebetween; said check valve member being located in the small end of said counterbalance valve member to engage an internal seat therein; and wherein another spring means between said check valve member and said partition means biases the former into engagement with said internal seat.
 9. The valve assembly of claim 8 wherein said spring means for biasing said counterbalance valve member extends into the large tubular end portion to bear on said counterbalance valve member; and wherein said closure means has adjusting screw means bearing on said spring means for varying the degree of biasing of said counterbalance valve member.
 10. A valve assembly comprising a body having a stepped bore terminating at its small end in a valve seat and a valve port for connection to a directional control valve, said body having a motor port and a pilot port leading to different diameter portions of said bore and adapted to be connected to the respective ports of a double acting fluid motor; a stepped counterbalance valve member in said bore spring biased into engagement with said seat to prevent return flow of fluid from said motor port to said valve port; said valve member having a first relatively small annular area defined between said valve seat and a first enlargement of said bore which is exposed to fluid pressure in said motor port, whereby fluid pressure of relatively large magnitude due to thermal expansion of the fluid or to motor load inertia or shock will overcome the spring bias to move said valve member away from said seat for relief of excess pressure through said motor and valve ports, and a second relatively large annular area defined between said first enlargement of said bore and a second enlargement thereof which is exposed to fluid pressure in said pilot port whereby fluid pressure in said pilot port of relatively low magnitude will overcome the spring bias to move said valve member as aforesaid for return flow of fluid from the motor through said motor and valve ports; and a check valve member movable in said counterbalance valve member to permit flow of fluid in the opposite direction from said valve port to said motor port. 